1,044 research outputs found
Trapping cold atoms near carbon nanotubes: thermal spin flips and Casimir-Polder potential
We investigate the possibility to trap ultracold atoms near the outside of a
metallic carbon nanotube (CN) which we imagine to use as a miniaturized
current-carrying wire. We calculate atomic spin flip lifetimes and compare the
strength of the Casimir-Polder potential with the magnetic trapping potential.
Our analysis indicates that the Casimir-Polder force is the dominant loss
mechanism and we compute the minimum distance to the carbon nanotube at which
an atom can be trapped.Comment: 8 pages, 3 figure
Isotopic difference in the heteronuclear loss rate in a two-species surface trap
We have realized a two-species mirror-magneto-optical trap containing a
mixture of Rb (Rb) and Cs atoms. Using this trap, we have
measured the heteronuclear collisional loss rate due to
intra-species cold collisions. We find a distinct difference in the magnitude
and intensity dependence of for the two isotopes Rb and
Rb which we attribute to the different ground-state hyperfine splitting
energies of the two isotopes.Comment: 4 pages, 2 figure
Quantitative study of quasi-one-dimensional Bose gas experiments via the stochastic Gross-Pitaevskii equation
The stochastic Gross-Pitaevskii equation is shown to be an excellent model
for quasi-one-dimensional Bose gas experiments, accurately reproducing the in
situ density profiles recently obtained in the experiments of Trebbia et al.
[Phys. Rev. Lett. 97, 250403 (2006)] and van Amerongen et al. [Phys. Rev. Lett.
100, 090402 (2008)], and the density fluctuation data reported by Armijo et al.
[Phys. Rev. Lett. 105, 230402 (2010)]. To facilitate such agreement, we propose
and implement a quasi-one-dimensional stochastic equation for the low-energy,
axial modes, while atoms in excited transverse modes are treated as independent
ideal Bose gases.Comment: 10 pages, 5 figures; updated figures with experimental dat
Dynamically controlled toroidal and ring-shaped magnetic traps
We present traps with toroidal and ring-shaped topologies, based on
adiabatic potentials for radio-frequency dressed Zeeman states in a ring-shaped
magnetic quadrupole field. Simple adjustment of the radio-frequency fields
provides versatile possibilities for dynamical parameter tuning, topology
change, and controlled potential perturbation. We show how to induce toroidal
and poloidal rotations, and demonstrate the feasibility of preparing degenerate
quantum gases with reduced dimensionality and periodic boundary conditions. The
great level of dynamical and even state dependent control is useful for atom
interferometry.Comment: 6 pages, 4 figures. Paragraphs on gravity compensation and expected
trap lifetimes adde
An Efficient Implementation of the Gauss-Newton Method Via Generalized Krylov Subspaces
The solution of nonlinear inverse problems is a challenging task in numerical analysis. In most cases, this kind of problems is solved by iterative procedures that, at each iteration, linearize the problem in a neighborhood of the currently available approximation of the solution. The linearized problem is then solved by a direct or iterative method. Among this class of solution methods, the Gauss-Newton method is one of the most popular ones. We propose an efficient implementation of this method for large-scale problems. Our implementation is based on projecting the nonlinear problem into a sequence of nested subspaces, referred to as Generalized Krylov Subspaces, whose dimension increases with the number of iterations, except for when restarts are carried out. When the computation of the Jacobian matrix is expensive, we combine our iterative method with secant (Broyden) updates to further reduce the computational cost. We show convergence of the proposed solution methods and provide a few numerical examples that illustrate their performance
Theoretical analysis of the implementation of a quantum phase gate with neutral atoms on atom chips
We present a detailed, realistic analysis of the implementation of a proposal
for a quantum phase gate based on atomic vibrational states, specializing it to
neutral rubidium atoms on atom chips. We show how to create a double--well
potential with static currents on the atom chips, using for all relevant
parameters values that are achieved with present technology. The potential
barrier between the two wells can be modified by varying the currents in order
to realize a quantum phase gate for qubit states encoded in the atomic external
degree of freedom. The gate performance is analyzed through numerical
simulations; the operation time is ~10 ms with a performance fidelity above
99.9%. For storage of the state between the operations the qubit state can be
transferred efficiently via Raman transitions to two hyperfine states, where
its decoherence is strongly inhibited. In addition we discuss the limits
imposed by the proximity of the surface to the gate fidelity.Comment: 9 pages, 5 color figure
Extracting Atoms on Demand with Lasers
We propose a scheme that allows to coherently extract cold atoms from a
reservoir in a deterministic way. The transfer is achieved by means of
radiation pulses coupling two atomic states which are object to different
trapping conditions. A particular realization is proposed, where one state has
zero magnetic moment and is confined by a dipole trap, whereas the other state
with non-vanishing magnetic moment is confined by a steep microtrap potential.
We show that in this setup a predetermined number of atoms can be transferred
from a reservoir, a Bose-Einstein condensate, into the collective quantum state
of the steep trap with high efficiency in the parameter regime of present
experiments.Comment: 11 pages, 8 figure
Quantum Scattering in Quasi-1D Cylindrical Confinement
Finite size effects alter not only the energy levels of small systems, but
can also lead to new effective interactions within these systems. Here the
problem of low energy quantum scattering by a spherically symmetric short range
potential in the presence of a general cylindrical confinement is investigated.
A Green's function formalism is developed which accounts for the full 3D nature
of the scattering potential by incorporating all phase-shifts and their
couplings. This quasi-1D geometry gives rise to scattering resonances and
weakly localized states, whose binding energies and wavefunctions can be
systematically calculated. Possible applications include e.g. impurity
scattering in ballistic quasi-1D quantum wires in mesoscopic systems and in
atomic matter wave guides. In the particular case of parabolic confinement, the
present formalism can also be applied to pair collision processes such as
two-body interactions. Weakly bound pairs and quasi-molecules induced by the
confinement and having zero or higher orbital angular momentum can be
predicted, such as p- and d-wave pairings.Comment: Extended version of quant-ph/050319
Ultra-High-Resolution Optical Coherence Tomographic Findings in Commotio Retinae
Commotio retinae is a self-limited opacification of the retina secondary to direct blunt ocular trauma. Histologic studies of monkeys and humans relate this clinical observation to damaged photoreceptor outer segments and receptor cell bodies.[superscript 1 - 3] Reports using time-domain optical coherence tomography (OCT) and spectral-domain OCT support the involvement of the photoreceptor layer, but these techniques lack the resolution necessary to confirm results of histologic analysis.[superscript 4 - 6] Prototype high-speed ultraâhigh-resolution OCT (hs-UHR-OCT) images demonstrate these anatomical changes in a patient with acute commotio retinae.National Institutes of Health (U.S.) (Contract Number RO1-EY11289-23)National Institutes of Health (U.S.) (Contract Number R01-EY13178-07)United States. Air Force Office of Scientific Research (Grant Number FA9550-07-1-0101)United States. Air Force Office of Scientific Research (Grant Number FA9550-07-1-0014
Multidirectional Subspace Expansion for One-Parameter and Multiparameter Tikhonov Regularization
Tikhonov regularization is a popular method to approximate solutions of linear discrete ill-posed problems when the observed or measured data is contaminated by noise. Multiparameter Tikhonov regularization may improve the quality of the computed approximate solutions. We propose a new iterative method for large-scale multiparameter Tikhonov regularization with general regularization operators based on a multidirectional subspace expansion. The multidirectional subspace expansion may be combined with subspace truncation to avoid excessive growth of the search space. Furthermore, we introduce a simple and effective parameter selection strategy based on the discrepancy principle and related to perturbation results
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